1. Field of the Invention
The invention relates to a display device which includes a driver circuit and a liquid crystal display with a plurality of rows R and columns C. The invention also relates to a driver circuit for driving a display.
2. Description of Related Art
The display technique will play an increasingly more important role in the information and communication technique in the years to come. Being an interface between humans and the digital world, the display device is of crucial importance for the acceptance of contemporary information systems. Notably portable apparatus such as. for example, notebooks, telephones, digital cameras and personal digital assistants cannot be realized without utilizing displays. The passive matrix LCD technology is a very commonly used LCD technology; it is used, for example, in laptops and in mobile telephones. The passive matrix display technology enables the implementation of large displays; such large displays are usually based on the (S)TN (Super Twisted Nematic) effect. A passive matrix LCD consists of a number of layers. The display is subdivided in the form of a matrix of rows and columns. The row electrodes and column electrodes that are arranged on respective substrates form a grid. The layer with the liquid crystal is provided between said substrates. The intersections of these electrodes, form image points or pixels. These electrodes are supplied with voltages that orient the liquid crystal molecules of the driven pixels in an appropriate direction so that the driven pixel becomes visible.
Since the size of the displays becomes larger, the significance of the power consumption of the passive matrix LCD displays for mobile applications increases all the time. Because such passive matrix displays are often used in portable apparatus, it is particularly important to realize a low power consumption. The effective deployment of a standby mode is a suitable approach to reducing the power consumption. For example, in mobile telephones all components that are not necessary are deactivated in such a standby mode. The display is then also switched to a partial display mode.
In addition to the power consumption, however, the optical performance of such STN LC displays is also a decisive criterion for the selection of display devices of this kind. For this type of STN LC display it is known to use an addressing technique where a plurality of rows is simultaneously driven and the encoded image information is applied to the columns. This MRA (Multiple Row Addressing) technique enables a very good optical performance to be achieved in combination with a low power consumption.
According to said MRA technique a number of p rows is simultaneously driven. A set of orthogonal functions is then applied to the simultaneously driven rows p. A function for driving the corresponding column is calculated from said set of orthogonal functions by way of a calculation rule. Using this function for driving the column, a voltage is selected from a plurality of partial voltage values, said voltage being applied to the corresponding column so that the corresponding pixels or image points are switched to an initial or starting state, that is, in dependence on the data that is supplied from a memory.
Not the entire display is driven in the partial display mode; this means that only sub-regions of the display are required for the display of information. In the case of addressing by means of the MRA technique, however, it is necessary to select an optimum value p of the number of simultaneously driven rows so as to achieve the best optical performance.
p+1 different voltages are required so as to drive p simultaneously driven rows. These voltages are generated by means of a plurality of voltage driver stages in a driver circuit for driving the display. The driver circuit is configured in such a manner that said driver circuits drive the maximum possible number p of rows that are to be simultaneously driven and also comprise a corresponding number of voltage driver stages.
Using such driver circuits it is not possible to influence the circuit in the partial display mode in such a manner that the saving of power is optimized. Moreover, such a driver circuit is capable of driving only a limited number of different display sizes.
Therefore, it is an object of the invention to provide a display device whereby the number p of rows of a display that are to be simultaneously driven can be adaptively selected with a reduced power consumption and for different display sizes.